Production of pigmented cellulosic pulp



Patented Jan. 29, 1952 William Lutton Craig, Westport, 1Conn., assignor to .R. T. Vanderbilt Company, .Inc., New York, N. Y., a corporation of .New iYOI'k No Drawing. Application March 17, 1948, Serial No. 15,509

.3 Claims.

This invention relates to the production of pigmented cellulosic :pulp by precipitating the pigment inserted in andon and around the fibers of the pulp in amount exceeding the weight of the fibers.

According to the present invention a highly pigmented fibrous product is produced by adding cellulosic fibers in the form of dry paper pulp 'to a dilute solution 'of calcium chloride, barium chloride or zinc chloride to form a pulp in such solution and mechanically working or beating such pulp to effect swelling and hydration and gelatinizing of the cellulosic fibers followed -by precipitation of an insoluble calcium, barium or Zinc pigment, particularly calcium carbonate, barium sulfate, zinc sulfate or hydroxide, etc. in and on and around the modified fibers by the addition of a soluble salt such :as sodium carbonate, sodium sulfate, etc.

.I have found that ordinary commercial waste calcium chloride liquor containing about 10% calcium chloride can advantageously be used in the production of fibrous pigments or pigmented fibers of high pigment content by aciding dry cellulosic fiber pulp to such liquor to form a suspension of such pulp therein and by mechanical working of the pulp with the solution in a beater or the like until the fibers are swollen and hydrated and converted into a gelatinous or gel-like form and by subsequent precipitation of an insoluble pigment, particularly calcium carbonate, within as well as on and around the thus modified fibers, particularly by the addition of a solution of sodium carbonate thereto.

I Commercial calcium chloride in a dry form is commonly produced from calcium chloride solutions by concentrations of such solutions to give the dry product. Dry calcium chloride can "be redissolved in water or in aqueous pulp solutions to form strong calcium chloride solu' ment of cellulosic fibers in pulp form by adding the dry calcium chloride to the aqueous pulp stock at a paper or pulp mill to elfect modi- 'fication of the fibers followed by precipitation of an insoluble pigment in and on and around the modified-fibers.

.I have found that the use of strong solutions of calcium chloride is not necessary, and that the-more dilute solutions of ordinary waste cal 'cium chloride liquor can be advantageously used by adding dry 'cellulosic pulp fibers thereto and particularly cellulosic fibers,

by prolonged mechanical working of the resulting :pulp to effect swelling and hydration and modification of the fibers to convert the fibers into a modified gelatinized or gel-like state with a minimum of ,free water around the fibers; and that valuable pigmented fibrous products can be obtained by then treating the gelatinized fibers with a solution :of a soluble salt such as sodium carbonate to precipitate an insoluble pigment such as calcium carbonate in and on and around the modified fibers, with subsequent removal of the by-product salt ,from the result ing pigmented product.

The dry pulp fibers which are used in the present process for making the fibrous pigment products include "various paper pulp fibers and including both chemical and semi-chemical pulp and groundwood fibers such as sulfite pulp, sulfate pulp, soda pulp, semi-chemical pulp, mechanical pulp, etc. The dry pulp stock may be bleached 101' unbleached stock and may be stock which .has been previously refined in a beater or refining engine or which may advantageously be unrefined stock, and which is converted into a refined stock by the mechanical treatment of beating or refining to which it is subjected in connection with the treatment of the dry pulp, after its addition to the dilute calcium chloride solution.

The proportions of dry cellulosic stock to dilute calcium chloride solution can be varied but (in general the amount of calcium chloride present in the dilute solution will advantageously be several times the weight of the stock treated lution containing about 10% of calcium chloride can 'be advantageously used for beating and hydrating and treating an amount of dry stock corresponding to a 2% stock (dry basis) in such solution, the amount of calcium chloride in this case being about five times the weight of the stock (dry basis) treated; and that the resulting modified and hydrated and gelatinized stock can then be treated with a sodium carbonate solution to form a fibrous pigment suspension containing a large amount of finely divided calcium carbonate pigment precipitated both within the fibers and on and around the fibers and amounting, e. g., to around 80% or more of the weight of the resulting fibrous pigment (dry basis).

The present process is well adapted for -use at locations where cheap by-product waste calweight of the fibers (dry basis).

cium chloride solutions are available, by shipping the dry pulp from the pulp or paper mill and by adding the dry pulp to such dilute solutions and subjecting the same to prolonged mechanical treatment therein.

The mechanical treatment of the pulp in such dilute solutions can be carried out in an ordinary beater, with or without refining of the pulp, but advantageously with refining of the pulp during the beating operation, or in combination with refiners through which the pulp is to a greater or less extent circulated to efiect refining of the pulp fibers in such solution. The prolonged mechanical working of the pulp is important and should be continued until the pulp fibers are swollen and hydrated and modified and converted into a gelatinous or gel-like state with a minimum of free water around the fibers and with a greater part of the water in the form of a solution contained within the swollen and gelatinized fibers; The refining of the pulp in connection with such treatment with the dilute calcium chloride solution not only promotes the swelling and hydration and gelatinizing of the fibers but also gives a refined pigmented fibrous product, at the end of the process, whichcan advantageously be added as a fibrous pigment to refined paper pulp for paper manufacture.

While the ordinary 10% waste solutions of calcium chloride are advantageously used in the present process, an even more dilute solution of calcium chloride can be used with the dry fibrous stock, particularly with dilute stock containing a small percentage of fibers (dry basis) provided the mechanical treatment is sufficiently prolonged to bring about the swelling and hydrating and modifying and gelatinizing of the fibers. For example, with a calcium chloride solution and with an added amount of dry fibers corresponding to a 1% or 2% stock (dr basis), and

with prolonged mechanical working or beating of the stock in such solution, followed by precipitation of the insoluble pigment in and on and around the modified fibers, a pigmented fi- 'brous product can be produced containing an amount of pigment greatly in excess of the With stocks of higher concentration, e. g., around 4% to 6% fibers, made from the dry paper pulp, stronger solutions, around 10% calcium chloride, are advantageously used.

The invention will be further illustrated by the following specific example:

Bleached sulfite pulp was added to a waste calcium chloride solution containing about 10% calcium chloride in amount sufiicient to form a pulp of around 2% fibers (dry basis) and the resulting pulp was subjected to mechanical working in a beater and with circulation of a portion of the pulp through a refiner and back to the beater until the fibers had been swollen and hydrated and converted into a gelatinous condition with a minimum of free water. Sodium carbonate was subsequently added to the resulting pulp in the form of a 10% solution and in amount sufficient to react with the calcium chloride to precipitate calcium carbonate. The reaction of the sodium carbonate solution brought about shrinking of the swollen hydrated fibers and resulted in the production of a highly pigmented fibrous product which after washing to remove by-product sodium chloride contained on a dry basis about 80% of calcium carbonate and about of modified fiber.

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The resulting fibrous pigment or pigmented fibrous product, after washing to remove the sodium chloride solution, can advantageously be used for addition to other paper pulp to pigment the same, giving a fibrous pigment which readily admixes with the untreated fibers. When the fibrous pigment is refined during the process of its production, the resulting fibrous pigment is a refined product which can be added to refined paper pulp shortly before its use on the paper machine for paper manufacture.

The fibrous pigment produced by the present process can advantageously be dried to give a dry fibrous pigment product which can be stored and shipped and used in a paper mill by adding it to water or to pulp to convert it into the form of aqueous pulp. Where such fibrous pigment is dried for storage or shipment the drying should be carried out without excessive overheating of the product, as by drying at moderate temperatures. Such dry fibrous pigments are more particularly described and claimed in my companion application Serial No. 15,510.

While in the above example the dry pulp treated was bleached sulfite pulp and the amount used was such as to give a stock of about 2% with the 10% calcium chloride solution, a more concentrated stock can be used, e. g., up to 5 or 6%, the practical range being from about 2% to around 6% or even as low as 1%, to give pigmented products which in a dry state would contain more pigment than fiber and advantageously several times as much pigment as fiber up to e. g. eight or more parts of pigment to one of fiber (dry basis) g So also, other stocks than bleached sulfite stock can be similarly used, including unbleached stock and other chemical, semi-chemical cr mechanical pulps which are produced at a pulp mill and shipped in a dry state for use'in the process. Unrefined pulps are advantageously used since they can be subjected to a refining treatment as part of the mechanical treatment of the pulp in the calcium chloride solution. The prolonged mechanical treatment to efiect swelling and hydrating and gelatinizing of the pulp fibers in the calcium chloride solution, when carried out with beating or refining of the pulp will give a refined pigmented fibrous product after the pigmenthasbeen precipitated therein.

While pigmented products can be made in 7 Which the amount of pigment does not greatly exceed the amount of fiber (dry basis) the process is particularly advantageous for producing fibrous pigments with several times as much pigment as fiber, particularly two or three or four times as much pigment as fiber, or even more (dry. basis) Such fibrous pigments will retain the fibrous character of the modified fibers but will have a large amount of finely divided precipitated pigment, largely precipitated within the fibers, and also on and around the fibers. And such fibrous pigments have the advantage that the loss of pigment from the paper stock is minimized when these pigments are admixed with untreated fibers and used for paper manufacture.

The fibrous pigments produced by the present process can advantageously be used in-making paper or for coating paper-, such as described in my prior applications SerialNos. 664,425 and Calcium carbonate is a particularly advantageous pigment in the newfibrous pigment product. It is readily produced when sodium carbonate is used for reaction with the calcium chloride to form the insoluble pigment. Other insoluble calcium pigments can similarly be produced, for example, by using sodium borate instead of sodium carbonate and precipitating insoluble calcium borate as the pigment in the fibrous pigment product.

Fibrous pigments or pigmented fibers containing precipitated barium and zinc pigments can be produced in a similar manner by the addition of dry pulp to a solution of barium chloride or zinc chloride with mechanical treatment to effect swelling and hydrating and gelatinizing of the pulp fibers in the barium chloride or zinc chloride solution followed by precipitation of the insoluble barium or zinc pigment by the addition of a soluble salt such as sodium sulfate or alum (aluminum sulfate) or other soluble sulfate, or by adding a soluble carbonate, etc. to precipitate insoluble barium r zinc sulfate or barium sulfate admixed with aluminum hydrate or barium or zinc carbonate or zinc silicate, or zinc hydroxide, etc.

The process in which barium chloride or zinc chloride is used is carried out as hereinbefore described in connection with calcium chloride by adding the dry pulp to the barium chloride or zinc chloride solution with mechanical treatment where needed to effect the hydrating and swelling and gelatinizing of the fibers so that a minimum of free water is present around the gelatinized fibers and by then precipitating the insoluble barium or zinc pigment by adding the soluble precipitating salt to the gelatinized stock.

While the process of the present invention is particularly advantageous with dilute solutions of calcium chloride, barium chloride and zinc chloride, more concentrated solutions can be used and the dry pulp can be added thereto and the swelling and hydrating and gelatinizing of the fibers accomplished with less mechanical treatment than when dilute solutions are used; and similar highly pigmented fibers or fibrous pigments can be produced containing an amount, e. g., of barium sulfate or barium sulfate and aluminum hydrate or barium carbonate or zinc sulfate or zinc carbonate or Zinc silicate or zinc hydroxide in amount exceeding the weight of the fibers (dry basis) and advantageously in amount two or three or four or five times the weight of the fibers. The highly pigmented fiber thus produced can similarly be used in admixture with ordinary paper pulp to form a pigmented paper: or the fibrous pigments can be treated under regulated conditions to give a dry fibrous pigment product.

I claim:

.1. method of producing pigmented cellulosic pulp which comprises adding cellulosic fibers to a calcium chloride solution to form a resultant pulp containing from about to calcium chloride and at least about 1% of fibers, subjecting the pulp to prolonged mechanical treatmaintaining the fibers in the calcium chloride solution until the combined effects thereof and the mechanical treatment have resulted in the fibers becoming swollen, hydrated and gelatinized, thereafter adding a soluble salt which will react with the calcium chloride to form a precipitated calcium compound pigment,

the amounts of the calcium chloride and said soluble salt being such as to precipitate within, on and around the modified cellulose fibers an amount of the calcium compound pigment in excess of the Weight of the modified on a dry basis.

2. The method of producing pigmented cellu losic pulp which comprise adding cellulosic fibers to a calcium chloride solution to form a resultant pulp containing about 10% calcium chloride and from about 1% to 6% of fibers, subjecting the pulp to prolonged mechanical treatment, maintaining the fibers in the calcium chloride solution until the combined effects thereof and the mechanical treatment have resulted in the fibers becoming swollen, hydrated and gelatinized, thereafter adding sodium carbonate to the resultant pulp to react with the calcium chloride to precipitate a calcium carbonate pigment in finely-divided form, the amounts of the calcium chloride and the sodium carbonate being such as to precipitate within, on and around the modified cellulose fibers an amount of the finely-divided calcium carbonate greatly exceeding the weight of the modified fibers, on a dry basis.

3. The method of producing pigmented cellulosic pulp which comprises adding cellulosic fibers to a chloride solution selected from the group consisting of calcium chloride, barium chloride and zinc chloride to form a resultant pulp containing from about 5% to 10% of such chloride and at least about 1% of fibers, subjecting the pulp to mechanical treatment, maintaining the fibers in such chloride solution until the combined effects thereof and the mechanical treatmcnt have resulted in the fibers becoming swolien, hydrated and gelatinized, thereafter adding a soluble salt which will react with such chloride to form a precipitated pigment in finely-divided form, the amounts of such chloride and said soluble salt being such as to precipitate within, on and around the modified cellulose fibers an amount of the pigment in excess of the weight of the modified fibers. on a dry basis.

WILLIAM LU'I'TON CRAIG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 354,477 Just et al. Dec. 14, 1886 821,434 Sachsenroder ....J. May 22, 1906 1,333,465 Clayton et al. Mar. 9, 1920 1,815,761 Cerini July 21, 1931 1,842,712 Bradley Jan. 26, 1932 2,315,892 Booth Apr. 6, 1943 2,457,797 Craig Jan. 4, 1949 FOREIGN PATENTS Number Country Date 404 Great Britain of 1869 151,381 Great Britain Sept, 27, 1920 516,162 Great Britain Dec. 22, 1939 OTHER REFERENCES Marsh et al., An Introduction to the Chemistry of Cellulose, Chapman and Hall, 1938, page 73. 

1. THE METHOD OF PRODUCING PIGMENTED CELLULOSIC PULP WHICH COMPRISES ADDING CELLULOSE FIBERS TO A CALCIUM CHLORIDE SOLUTION TO FORM A RESULTANT PULP CONTAINING FROM ABOUT 5% TO 10% CALCIUM CHLORIDE AND AT LEAST ABOUT 1% OF FIBERS, SUBJECTING THE PULP TO PROLONGED MECHANICAL TREATMENT, MAINTAINING THE FIBERS IN THE CALCIUM CHLORIDE SOLUTION UNTIL THE COMBINED EFFECTS THEREOF AND THE MECHANICAL TREATMENT HAVE RESULTED IN THE FIBERS BECOMING SWOLLEN, HYDRATED AND GELATINIZED, THEREAFTER ADDING A SOLUBLE SALT WHICH WILL REACT WITH THE CALCIUM CHLORIDE TO FORM A PRECIPITATED CALCIUM COMPOUND PIGMENT, THE AMOUNTS OF THE CALCIUM CHLORIDE AND SAID SOLUBLE SALT BEING SUCH AS TO PRECIPITATE WITHIN, ON AND AROUND THE MODIFIED CELLULOSE FIBERS AN AMOUNT OF THE CALCIUM COMPOUND PIGMENT IN EXCESS OF THE WEIGHT OF THE MODIFIED FIBERS, ON A DRY BASIS. 